Ostia Antica
Near the airport in Rome, the ancient port city of Ostia Antica offers visitors an amazing array of roman houses, stores, temples, and other public areas. Altough the 'excavation' undertaken by Mussolini in the 1930's damaged much of the post-Imperial evidence, and the elements are doing their best to damage the early 20th century excavations, there is still much to see. I would consider this one of the "must-see" areas of the Roma-Napoli region.
The agency responsible for the area has a great website you can visit for more information: http://www.ostia-antica.org/